1. Technical Field
The present disclosure relates to an inverter for a liquid crystal display (LCD) device.
2. Description of Related Art
LCD devices provide portability, low power consumption, and low radiation, and find wide use in various portable information devices such as notebooks, personal digital assistants (PDAs), video cameras and others. A typical LCD device includes an LCD panel, one or more backlights illuminating the LCD panel, and an inverter driving the backlights.
FIG. 3 shows a circuit diagram of a commonly used inverter. The inverter 10 includes a pulse width modulation (PWM) circuit 11, a first transistor 13, a second transistor 12, a direct current (DC) voltage input terminal 14, a first transformer 15, and a second transformer 16. The PWM circuit 11 includes a first output terminal 112 and a second output terminal 111. The first transformer 15 includes a first primary winding 151 and a first secondary winding 152. The first primary winding 151 includes a first terminal 1511 and a second terminal 1512. The second transformer 16 includes a second primary winding 161 and a second secondary winding 162. The second secondary winding 162 includes a third terminal 1611 and a fourth terminal 1612. The DC voltage input terminal 14 receives a fourteen volt (14V) DC voltage.
A gate electrode (not labeled) of the second transistor 12 is connected to the second output terminal 111 of the PWM circuit 11 via a resistor. A source electrode (not labeled) of the second transistor 12 is grounded. A drain electrode (not labeled) of the second transistor 12 is connected to a source electrode (not labeled) of the first transistor 13. A gate electrode (not labeled) of the first transistor 13 is connected to the first output terminal 112 via a resistor. A drain electrode (not labeled) of the first transistor 13 is connected to the DC voltage input terminal 14.
The first terminal 1511 of the first primary winding 151 is connected to the drain electrode of the second transistor 12. The second terminal 1512 of the first primary winding 151 is connected to the DC voltage input terminal 14 via a capacitor, and grounded via a storage capacitor 17. Two terminals (not labeled) of the first secondary winding 152 are connected to two lamps (not labeled), respectively. The third terminal 1611 of the second primary winding 161 is connected to the first terminal 1511 of the first primary winding 151. The fourth terminal 1612 of the second primary winding 161 is connected to the second terminal 1512 of the second primary winding 151. Two terminals (not labeled) of the second secondary winding 162 are connected to other two lamps (not labeled), respectively. The four lamps provide a light source for the LCD device.
When the inverter 10 is operational, the PWM circuit 11 alternates between outputting control signals to the gate electrode of the second transistor 12 and to the gate electrode of the first transistor 13, and the second transistor 12 and the first transistor 13 are switched on in turn.
When the second transistor 12 is switched off and the first transistor 13 is switched on, the 14V DC voltage charges the storage capacitor 17 via the first transistor 13 and the first primary winding 151 in turn. Simultaneously, the 14V DC voltage charges the storage capacitor 17 via the first transistor 13 and the second primary winding 161 in turn.
When the second transistor 12 is switched on and the first transistor 13 is switched off, the storage capacitor 17 discharges via the first primary winding 151 and the second transistor 12. Simultaneously, the storage capacitor 17 discharges via the second primary winding 161 and the second transistor 12.
However, when the first transistor 13 is switched on, current through the drain electrode and the source electrode of the first transistor 13 increases gradually, as voltage between the two electrodes decreases gradually, necessitating an overlap between the current and the voltage. Therefore, a high wattage loss of the first transistor 13 is generated when the first transistor 13 is switched on.
What is needed, therefore, is an inverter which can overcome the described limitations.